1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting and receiving control information in a wireless communication system.
2. Discussion of the Related Art
A description will first be made of a conventional method for transmitting control information in a wireless communication system. In an Institute of Electrical and Electronics Engineers (IEEE) 802.16e system, a Base Station (BS) allocates resources to a Mobile Station (MS) that has requested a bandwidth by a ranging code, using a Code Division Multiple Access (CDMA) allocation Information Element (IE).
Ranging codes are classified into four subsets according to the purposes that they serve, specifically initial ranging, handover ranging, periodic ranging, and bandwidth request. Conventionally, a plurality of ranging codes are generated and classified into four subsets according to their purposes. Thus the ranging codes have different indexes.
[Table 1] below illustrates a CDMA allocation IE.
SizeSyntax(bit)NotesCDMA_Allocation_IE( ) {——Duration6—UIUC4UIUC for transmissionRepetition Coding20b00: No repetition codingIndication0b01: Repetition coding of 2 used0b10: Repetition coding of 4 used0b11: Repetition coding of 6 usedFrame Number Index4LSBs of relevant frame numberRanging Code8—Ranging Symbol8—Ranging subchannel7—BW request mandatory11: Yes0: No}——
In [Table 1], Duration indicates the amount of resources that a BS allocates to an MS by the CDMA allocation IE, in Orthogonal Frequency Division Multiple Access (OFDMA) symbols. Repetition Coding Indication specifies a coding rate of data that the MS is supposed to transmit in the allocated resources.
Frame Number Index identifies a frame in which the UE transmitted a CDMA code by four Least Significant Bits (LSBs) of a frame number.
Ranging Code specifies the CDMA code transmitted by the UE and Ranging Symbol indicates an OFMA symbol carrying the CDMA code transmitted by the UE. Ranging Subchannel indicates a ranging subchannel in which the MS transmitted the CDMA code.
In an IEEE 802.16m system which is recently under standardization, an Advanced BS (ABS) transmits unicast service control information to an Advanced MS (AMS) by an Advanced MAP (A-MAP). The unicast service control information includes user-specific control information and non-user-specific control information. The user-specific control information is further divided into resource assignment information, Hybrid Automatic Repeat reQuest (HARQ) feedback information, and power control information. The resource assignment information, the HARQ feedback information, and the power control information are transmitted respectively in an assignment A-MAP, an HARQ A-MAP, and a power control A-MAP. All A-MAPs share a region of physical resources, called A-MAP region.
Each A-MAP IE includes a 16-bit Cyclic Redundancy Check (CRC).
With reference to FIG. 1, how an ABS appends a CRC to an A-MAP IE will be described below.
FIG. 1(a) illustrates an ABS's operation for masking a CRC by a Station ID (STID) and FIG. 1(b) illustrates an ABS's operation for masking a CRC by a Random Access ID (RAID). The term “STID” covers both an ID allocated to a particular AMS and an ID allocated commonly to a plurality of AMSs, in its meaning.
Referring to FIGS. 1(a) and 1(b), the ABS generates a CRC using a cyclic generator polynomial, masks the CRC by a 12-bit STID or a 12-bit RAID, and appends the resulting Masked CRC (MCRC) to input data. Specifically, the ABS appends a CRC masked with an STID of an identified AMS (i.e. an MCRC) to an A-MAP IE destined for the AMS, whereas it appends a CRC masked with a RAID (i.e. an MCRC) to an A-MAP IE destined for an anonymous UE. A RAID is generated according to random access attributes which are the indexes of time and frequency in which an AMS transmitted a code, and the index of the code.
FIG. 2(a) illustrates an AMS's operation for masking a received MCRC by an STID and FIG. 2(b) illustrates an AMS's operation for masking a received MCRC by an RAID.
Referring to FIGS. 2(a) and 2(b), upon receipt of an A-MAP IE, the AMS decodes the A-MAP IE and calculates a 16-bit MCRC of the A-MAP IE using a cyclic generator polynomial. The AMS then masks the 16-bit MCRC by its STID. Specifically, if the result of masking the MCRS with the STID is zero, the AMS determines that the ABS transmitted the A-MAP IE for the AMS and reads the remaining fields of the A-MAP IE.
In the case where the AMS has attempted a random access and is awaiting reception of a response to the random access attempt, if the result of masking the MCRS with the STID is non-zero, the AMS masks the MCRC with an RAID. If the result of masking the MCRC with the RAID is zero, the AMS determines that the ABS transmitted the A-MAP IE for the AMS and reads the remaining fields of the A-MAP IE.
When the AMS has not attempted a random access and the result of masking the MCRC by the STID is non-zero, or when the AMS has attempted a random access and the result of masking the MCRC by the RAID is non-zero, the AMS ignores the A-MAP IE.
According to the conventional technology, however, when the STID of an AMS is identical to the RAID of another AMS or when the RAID of an AMS that has transmitted a ranging code is identical to the RAID of an AMS that has transmitted a bandwidth request code, the AMS may recognize that an A-MAP IE destined for another AMS is for its own.
The same problem may be encountered when an A-MAP IE has a decoding error, in spite of different IDs for AMSs. For example, although an ABS transmits to AMS A an A-MAP IE including a CRC (i.e. MCRC) masked by the STID of AMS A, AMS B may mistake the A-MAP IE for an A-MAP IE including a CRC (i.e. MCRC) masked by its RAID due to wrong decoding.
In the IEEE 802.16e system, different indexes are assigned to all codes because codes designed in the same manner are classified into four subsets according to their purposes. Compared to the IEEE 802.16e system, bandwidth request codes and ranging codes are separately designed in the IEEE 802.16m system. As a consequence, some bandwidth request codes may have the same indexes as ranging codes. In addition, an ABS that has received a bandwidth request code and an ABS that has received a ranging code transmit uplink allocation information to AMSs in the same type of A-MAP IEs.
Another cause of the above problem is that the same CRC is masked with different IDs under circumstances.